CARET is an ongoing double-blind lung cancer chemoprevention trial of the efficacy and safety of the combination of 30 mg beta-carotene and 25,000 IU retinyl palmitate daily in two high-risk populations: (a) male and female current and former smokers recruited primarily from insurance-based sources, and (b) males with extensive occupational asbestos exposure recruited primarily from employment-based sources. We have documented successful recruitment, excellent compliance, and minimal side effects, in over 15,000 participants randomized thus far at six study Centers. Through 30 April, 1993, CARET has randomized 4,000 asbestos-exposed workers, exceeding accrual goals at all five CARD asbestos centers, and 11,105 heavy smokers. Seattle and Portland have exceeded their heavy smoker goals, and Irvine is on track to achieve its goal in July 1994. During the final five-year period, CARET will focus on retention, adherence to protocol, ascertainment of endpoints, monitoring of key design parameters, closeout of the trial, and analysis and publication. Projections indicate that with 14,240 smokers and 4,010 asbestos-exposed participants and 114,100 person-years of follow-up through February 1998, CARET will be capable of detecting a 23% reduction in lung cancer incidence in the two high-risk populations combined, and 27%, 49%, 32%, and 35% reductions in the smokers, female smokers, male smokers, and asbestos-exposed subgroups, respectively. The University of Maryland Occupational Health Project received funding to initiate a Baltimore Study Center as part of CARET in October 1988. Recruitment and randomization of 808 asbestos-exposed participants was completed in February 1992; up to 20 participant spouses who themselves meet the criteria for heavy smokers are being recruited in year 5. During the final five year period the Baltimore Study Center will maintain the current high rates of study vitamin adherence and active participation. Staff will focus on retention and ascertainment and confirmation of primary and secondary endpoints. Specific preparations for study closeout and for analysis of data and dissemination of results will occur during the last two years.